Basic-Naked Pairs

A Naked Pair (also known as a Conjugate Pair) is a set of two candidate numbers sited in two cells that belong to at least one unit in common. That is they reside in the same row, box or column.

It is clear that the solution will contain those values in those two cells and all other candidates with those numbers can be removed from whatever unit(s) they have in common.

Figure 1
Consider this center box in Figure 1. There are two 4/7s at A and B. Two other cells contain 4s and 7s. We remove those to produce the right hand picture.

Figure 2

Figure 2 is the same example but we're looking down the column at our two 4/7s at A and B. In the box below are two cells C and D which also contain 4s and 7s. We can safely remove the 4 from C and the 4 and 7 from D.